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Aisin 450-43LE transmission
450-43LE transmission is a four
speed computer controlled
transmission with converter
lock up found in Isuzu NPR, NQR
trucks, GM W3500 and
W4500 trucks Nissan
UD trucks and
Mitsubishi Fuso trucks
The recommended fluid for the Aisin 450-43LE transmission is DexronIII.
For some Free technical information such as
pressure testing transmission, component locations, applied elements and some simple tests you can perform on the
Aisin 450-43LE transmission please follow this
LINK to view PDF document.
Transmission goes into reverse
ok, when put into drive, seems like slipping or sluggish. pull shifter to low
and goes in 1st and off you go! go to 2nd and shifts to 2, drive and you have
3rd, harsh shifts on all. will not have o/d and lock up, stop and stays in 3rd
unless you pull manual low again.
Cause: likely blown
trans. fuse. (can be other power or failed Tcm problems) Mitsubishi
truck and fuses
are in the fuse panel. Isuzu truck strong and GM hide the fuse: remove glove box and look to
the left, wrapped up in harness are two fuses. one is for the transmission Tcm
power. you may notice that the o/d cancel light and trans lights do not work
Transmission goes into reverse
ok, when put in drive wont move or intermittently wont move. when put into low 1
off you go and can then up shift to 2nd,3rd and o/d and lock up all works fine
until you come to stop again and happens all over.
low Sprague inside transmission has or is failing. this requires disassembly and or
overhaul of the unit. can be mistaken as electrical problem but is not. will
require total disassembly and or rebuild of transmission. Planetary part number
from Isuzu: 8-97257013-0 and Isuzu part number for sprague is
Complaint: Transmission will not shift
out of first gear at all.
Cause: two possibilities;
one is both speed sensor 1 and 2 are not working, thus Tcm doesn't know truck is
moving (should be trouble codes set) or debris from internal failure or if
replaced unit already may be from cooler etc has gotten into valve body and
stuck shift valves and so on. (this may require an overhaul) Good way to test
this is unplug trans. harness and drive truck. should start in 3rd when in
drive, pull 2 and have 2, low have 1st. if this works then you don't have stuck
valves etc internally.
fluid is severely burnt, unit overheating very badly in short time of driving,
slipping, may not move at all.
Cause: possible cooler
restriction, can be due to cooler lines hooked up backwards to filter adapter on
Isuzu/Gm trucks, Thermostat stuck or damaged on Mitsubishi trucks, kinked lines,
clogged cooler. Mitsubishi trucks also have stand alone cooler and fan,
switch, which can be failed fan, switch etc and will cause severe overheating!
there's test explained in diagnostic information we offer for these trucks under
in the 450-43LE section. Its also very common someone has installed lines at filter head, backwards thus deadheading the cooler flow thru unit. this makes a very distinct
odor and can ruin the transmission!
Engine stalls when
into gear, no lock up, pressure problems (slipping) fluid may be very
clean if caught soon enough, no codes.
Cause: can be
cutback valve sleeve in valve body has broken which can cause any or all of the
above issues. can also ruin unit if run too long. Sonnax makes kit to repair:
Severe leak out
of front seal area, after removing unit you may find converter hard to remove,
stuck, and or comes out with pump bushing stuck to hub.
Cause: first and obvious one is an alignment issue of some sort,
can have flex plate assembled incorrectly causing this, Mitsubishi
can be missing alignment dowels in bell to engine holes, worn pilot bushing in
rear of crank, broken flex plates-loosened up bolts etc. if bushing seems welded
to hub can be bad ground from battery to frame, or engine to frame and what
happens is when cranking starter all those Amps are going thru the transmission
and arcing like an arc welder between the converter hub and pump bushing which
equals transmission destruction!
Transmission wont shift
up unless foot taken off throttle or shifts very late, may or may not have TPS
Cause: this scenario usually means the throttle cable
from pedal to injector pump linkage is loose. depending on how loose is how late
may be shifting or not at all. reason for this is TPS is inside cab on pedal
assembly, you have pedal and TPS floored and engine is actually maybe only 1/2
throttle. adjust throttle cable so there's no slack in it. this can be adjusted
under cab by linkage bracket.
Isuzu and GM trucks code 21 TPS. TPS, Throttle relearn procedure
After TPS, TCM replacement or battery discconect you may have code 21 for TPS range set and cannot clear or adjust TPS or find problem. there is TPS relearn procedure for
Isuzu and GM trucks.
TPS relearn procedure
Sprague or one way clutch rotation direction for Aisin 450-43LE transmission.
to view PDF file of both overdrive sprague and low reverse sprague proper roation and hold directions.
Mitsubishi Fuso Aisin transmission cooler thermostat assembly instructions
Workshop manual don't show correct assembly for transmission cooler thermostat.
Here is correct cooler
thermostat assembly picture
for Aisin transmissions.
Vehicle speed sensor code for either speed sensor 1 or sensor 2 in memory but
truck works fine with no problems.
Cause: one of
sensors is dead, Ckt open etc. this will not effect the operation of
transmission but if the
other sensor goes bad etc you will not be shifting at all! should be fixed,
there's two of them, ones for backup if other fails.
We offer Free transmission
diagnostic help for Aisin transmissions via E-Mail